1. Field of the Invention
The present invention relates to a voltage generator adapted for a flash memory.
2. Description of Related Art
In flash memories, for example, NOR flash memories, an internal voltage source is often required to provide an operating voltage. This voltage source is often generated through a charge pump circuit and a voltage regulator. The charge pump circuit is used to provide a relatively high output voltage to the voltage regulator, whereas the voltage regulator generates the power that the flash memory needs according to the output voltage.
Conventionally, the charge pump circuit generates the output voltage usually by multiplying the reference voltage by a fixed factor. In order to meet the maximum power need of the flash memory, the charge pump circuit is designed to provide a relatively high output voltage. However, when the power needed by the flash memory decreases, the output power generated by the charge pump circuit is not changed, which imperceptibly causes a waste of power. On the other hand, in such a case where there is a big difference between the output voltage received by the regulator and the voltage generated by the voltage regulator, a severe ripple phenomenon is occurred in the generated power. That is, the power generated by the voltage regulator mentioned above has a poor quality.